1. Field of the Invention
The present disclosure relates to a direct current power supply circuit.
2. Description of the Related Art
Switching power supply devices have widely been used for electronic devices such as home electric appliances or business machines for improving power conversion efficiency. Such power supply devices include semiconductor devices that utilize a switching operation by a semiconductor (a switching element such as a transistor) to control an output voltage.
Recently, it has attracted attention to a reduction in power consumption of these electronic devices upon a stand-by mode, and this trend generates a great demand for a switching power supply device that enables the reduction in power consumption upon a stand-by mode. Reduction in electric power supplied to a control circuit in a switching power supply device is effective way for reducing power consumption upon a stand-by mode.
A series-regulator direct current power supply circuit which acquires a direct-current voltage from an alternating-current voltage of a commercial power supply is often used to supply electric power to the control circuit in the switching power supply device. However, a voltage of a commercial power supply is an extremely high alternating-current voltage such as AC 100 V to 240 V, relative to a direct-current voltage of DC 5 V to 24 V needed for the control circuit. Therefore, a power loss of the direct current power supply circuit might be increased.
As a method of reducing a power loss of a direct current power supply circuit, a method has been proposed in which a full-wave rectification is performed after an alternating-current voltage from a commercial power supply is lowered with a transformer, and the resultant is converted into a direct-current voltage (see, for example, Unexamined Japanese Patent Publication No. S61-206016). As another method, there has been proposed a method in which it is detected that a rectified voltage formed by rectifying an alternating-current voltage from a commercial power supply becomes equal to or less than a first voltage, and a capacitor connected to a power supply terminal of a control circuit is charged during a period till the rectified voltage is inverted from 0 V and exceeds the first voltage to be equal to or larger than a second voltage (see, for example, Unexamined Japanese Patent Publication No. 2011-244602).